The present invention relates to a touch panel input device. Command input data is entered by pressing the surface of a transparent plate with a pen, finger, or the like. An electrical impulse is generated corresponding to the position of the pressure point and is sent to a processing device. More specifically, the present invention relates to a touch panel input device that enhances visibility by sealing a transparent insulative liquid between transparent plates. In general, touch panel input devices are found on the display screens of liquid crystal panels, CRTs, or the like. The operational surface of the touch panel input device is pressed while viewing the display information. The pressed position is detected and interpreted as command input data corresponding to the displayed content. The command input data is then sent to a processing device.
Touch panel input devices generally consist of a movable plate laminated over a substrate plate with an intervening insulative gap. Both the movable plate and the substrate plate have conductive layers covering their surfaces. The conductive surfaces are arraigned to face each other. The conductive surfaces are made from a transparent material which allows the underlying display screen to be viewed through them. There is a large difference between the refractive index of the air in the insulative gap and the refractive indices of the substrate and the movable plate. The difference in the refractive indices results in a transmittivity of only about 80% The reduction of the transmitted light makes the underlying display screen difficult to view.
Referring to FIGS. 5 and 6, a conventional touch panel input device 100 consists of a movable thin transparent plate 101, and a thick transparent plate 102 that is mounted up against a display device (not shown.) The two transparent plates, 101 and 102 are laminated together with a slight gap using a frame-shaped spacer 105.
Both facing surfaces of the transparent plates 101 and 102, are coated with smooth transparent conductor layers 103 and 104, of uniform thickness consisting of an indium tin oxide (ITO) film or other suitable transparent conductors. Leads 103a, 103b, 104a, and 104b are electrically connected on both sides of smooth transparent conductor layers 103 and 104 respectively. The voltage is read at a contact position between smooth transparent conductor layers 103 and 104 and the voltage corresponds to the pressed position on the surface of movable thin transparent plate 101.
Smooth transparent conductor layers 103 and 104 are usually separated by a frame shaped spacer 105. Dot spacers 106 which are composed of an insulative composite resin such as epoxy resin, are also affixed to transparent conductor layer 104 at appropriate intervals to prevent accidental contact between smooth transparent conductor layers 103 and 104. Dot spacers 106 often prevent the pressed position from being detected if the radius of curvature of the pressing device, as is the case when using a finger, is large. This also prevents accidental input from being detected when a person holding a stylus accidentally touches the surface of touch panel input device 100. This is referred to as a slip-of-the-hand operation.
The top and bottom surfaces of frame shaped spacer 105 are glued by an adhesive to the perimeter of smooth transparent conductor layers 103 and 104, sealing in the space between smooth transparent conductor layers 103 and 104. A transparent insulative liquid 107 is injected into the space between smooth transparent conductor layers 103 and 104.The refractive index of the transparent insulative liquid 107 is closer to the refractive index of the smooth transparent conductor layers 103 and 104 than it is to the refractive index of air. Because the difference between the refractive indices of the transparent insulative liquid 107 and the smooth transparent conductive layers 103 and 104 is less than the difference between the refractive indices of air and the smooth transparent conductor layers 103 and 104 , the amount of light transmitted through the touch panel input device 100 is improved.
This difficulty is addressed in, for example, Japanese unexamined patent application publication number S64-14630(1989) and Japanese unexamined patent application publication number H2-105916 (1990), which disclose a touch panel input device in which a transparent, insulative liquid that has a refractive index that is relatively close to that of the substrate and movable plate, is injected between them and sealed. Use of an insulative liquid with a comparable refractive index both lowers reflectivity and improves transinittivity.
When an insulative liquid such as silicon oil is used, transmittivity can be increased to about 90%. The underlying display screen is much easier to read because it appears brighter and has less glare.
Unfortunately, while improving transmittivity, the introduction of the insulative liquid leads to other problems, especially when the touch panel input device is operated in a tilted position. When the touch panel input device is operated in a generally vertical orientation, the insulative liquid between the two plates settles downward under its own weight. This produces a near vacuum in the upper section, allowing the facing surfaces of the transparent plate and the transparent substrate to approach each other within several microns. The close proximity of the two plates leads to false command data input being sent to the processor, even though the screen is not being pressed.
In addition to the above problem, when the screen is pressed, it is more difficult to bring the moveable transparent plate in contact with transparent substrate, because of the presence of the insulative liquid. The insulative liquid increases the pressing force required to operate the device. Devices that increase the pressure by applying the force over a smaller area, such as a stylus pen, can be used to overcome this problem, but this solution does not help when operating the touch panel with a finger, as is often desirable. Because the force is spread out over a greater area when using a finger, the pressure applied to the moveable transparent plate is decreased making it difficult to detect the pressed position. Because of this, operations such as writing text, drawing figures, or dragging the cursor on the display screen using only a finger is very difficult.
In view of the above discussion, it is an object of the present invention to overcome the drawbacks of the prior art.
It is a further object of the present invention to provide a touch panel input device that utilizes a light pressing force, without malfunctioning, even if the device as a whole is tilted and even if the input is done with a finger.
Briefly stated, the present invention provides a transparent insulative liquid sealed between two transparent plates that are coated with transparent conductor layers on their mutually facing surfaces of a touch panel input device. The facing surface of at least one of the transparent plates is roughened. Because the conductor layer is applied directly over the roughened surface of the transparent plate, the conductor layer is also roughened. When the entire device is tilted, the insulative liquid settles downward allowing the upper conductor layers to come into contact with each other, but because the surface is roughened only the protrusions of the conductor layer make contact. The overall contact resistance does not decrease sufficiently to be interpreted as a pressing operation. When a pressing operation is made, the insulative liquid flows into the depressions created by the roughened surface of the conductor layer. Because the liquid is not interposed between conductor layers, sure contact is made, and the pressed position requires only a light pressing force.
According to an embodiment of the invention, there is provided a touch panel input device comprising: an outer transparent plate that has an outer transparent plate first surface and an outer transparent plate second surface; the outer transparent plate is flexible, an inner transparent plate having an inner transparent plate first surface and an inner transparent plate second surface; the outer transparent plate second surface and the inner transparent plate first surface face each other to form mutually facing surfaces; the outer transparent plate and the inner transparent plate where at least one of the mutually facing surfaces is a roughened surface; a first transparent conductive layer coating the outer transparent plate second surface; a second transparent conductive layer coating the inner transparent plate first surface; a flexible seal interposed between the mutually facing surfaces; a transparent insulative liquid; the transparent insulative liquid is interposed between the mutually facing surfaces, and a position detection means electrically connected to the first conductive layer of the outer transparent plate and the second conductive layer of the inner transparent plate to interpret a contact position when the first transparent conductor layer is pressed against the second transparent conductive layer.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.